1. Field of the Invention
The present invention relates generally to image formation processes and apparatus using electrophotographic developing technology and, more particularly, to a developer preferably used in such processes and apparatus while using contact-type, single component and non-magnetic developing technology capable of developing an image by applying non-magnetic toner onto an electrostatic latent image that has been formed on the exterior circumferential surface of a photosensitive drum.
2. Description of the Prior Art
As well known to those skilled in the art, electrophotographic developing technology has been effectively and widely used in various picture producing apparatus, such as copying machines, laser beam printers, and plain paper facsimiles for converting optical image signals bearing data corresponding to images onto a tangible medium such as a cut sheet of paper. These images are processed with electrophotographic developing technology by a sequence of electrification, exposure, development, transcription and fixation on the printed medium. The engine mechanism of a typical example of a picture producing apparatus using an electrophotographic developing technique includes a photosensitive drum, a developer and a transfer roll. The developer usually has an electrifying roll, a developing roll, a toner feeding roll, a toner regulating blade and a toner agitator.
The agitator is installed in the toner tank of the developer and agitates new and remaining toner at a position around both the developing and feeding rolls, thus effectively mixing the new toner and the remaining toner together. The toner, applied on the developing roll, is regulated by the toner regulating blade. Toner on the developing roll is moved and attached to the exposure area of the photosensitive drum due to static electricity formed by a potential difference between the exposing potential of the drum and the developing potential of the roll, thus developing an image.
During the operation of the printer, the toner on the developing roll is partially moved onto the photosensitive drum. The toner on the developing roll is partially used at every revolution of the roll while the remaining toner kept on the roll remains unused. The developer is designed to remove the remaining toner from the developing roll by the rotation of a toner feeding roll at the nip between the two rolls after every revolution of the developing roll. When a developer is used for a lengthy period of time, however the expected operational function of the toner feeding roll may be deteriorated due to frictional abrasion of the roll's surface or an infiltration of the sponge used to make the roll's circumferential surface. In such a case, the toner feeding roller may fail to effectively remove such remaining toner from the developing roll, allowing the remaining toner to be frictionally electrified again at the nip between the developing roll and the feeding roll prior to being reused in a continued development step. Therefore, the frictional electrification of the developer for the toner may be reduced and fail to allow uniform distribution of the electrified bias voltage for each part of the developer, thereby reducing the quality of images printed upon each sheet of paper. Various schemes have been advocated in the art such as the Fixing Device Having A Cleaning Blade of Takayuki Seki, U.S. Pat. No. 5,625,442; the Cleaning Device For An Image Forming Apparatus of Motoharu Miki et alii, U.S. Pat. No. 5,678,134; the Image Forming Apparatus Employing Residual Toner Recovery Scheme of Yasuo Takuma, U.S. Pat. No. 5,701,570; and the Developing Device For An Image Forming Apparatus of Toshihiro Sugiyama, et alii, U.S. Pat. No. 5,708,942. Invariably, these schemes require modification, albeit however minor, of the operational sequence of the developer, and tend to lack backward compatibility enabling use of the developer, with a pre-existing image formation apparatus.